AbstractColor

Returns the color's channel values in its native color space. The channel names
and value ranges depend on the color space:
- sRGB: ['r', 'g', 'b'] (0-1)
- Oklab: ['l', 'a', 'b'] (l: 0-1, a/b: unbounded)
- Oklch: ['l', 'c', 'h'] (l: 0-1, c: 0+, h: 0-360)
- Lab: ['l', 'a', 'b'] (l: 0-100, a/b: unbounded)
- Lch: ['l', 'c', 'h'] (l: 0-100, c: 0+, h: 0-360)
- XYZ: ['x', 'y', 'z'] (unbounded)
- Display P3: ['r', 'g', 'b'] (0-1)

The alpha channel is accessed separately via getAlpha().

This is particularly useful for CSS Relative Color Syntax or custom color
manipulations where you need direct access to channel values.

Examples:
- Color::parse('red')->getChannels() // ['r' => 1.0, 'g' => 0.0, 'b' => 0.0]
- Color::parse('oklab(0.5 0.1 -0.2)')->getChannels() // ['l' => 0.5, 'a' => 0.1, 'b' => -0.2]

Returns a CSS-compatible color string. The output format depends on the space parameter:
- null (auto): Uses the most appropriate format for this color space
- 'srgb' or 'rgb': rgb() function
- 'hsl': hsl() function (for sRGB colors)
- 'color': color() function with explicit color space
- 'oklab', 'oklch', 'lab', 'lch': Respective CSS color functions

Examples:
- ->toCss() => 'rgb(255 0 0)' or 'oklab(0.628 0.225 0.126)'
- ->toCss('hsl') => 'hsl(0 100% 50%)'
- ->toCss('srgb') => 'rgb(255 0 0)'
- ->toCss('color') => 'color(srgb 1 0 0)'

Alpha channel is included in output when not fully opaque (< 1.0):
- 'rgb(255 0 0 / 0.5)' or 'oklab(0.628 0.225 0.126 / 0.8)'

Convenience method for converting to sRGB, the most common color space for web use.
This method is used internally by many operations that need to work in sRGB space.